Hey for those of you who are just starting to study, I recommend doing a PowerPrep test. The majority of these questions are from the OG so you can get a really good indication of where you are. I took this test after doing all of the OG problems (both the supplements) and thought I wasted my time since I was basically redoing problems and rememberd most of the Verbal answers.
The PowerPrep test was created by the old makers of the GMAT and GMATPrep is made by the new providers. Either way, both set of test are free. You can download GMATPrep
from mba.com and you can get PowerPrep by searching google (it'll be at gorilla something or other). People have said the GMATPrep is a very very good indicator for what you'll score on the real thing but you only have two chances to take it when you really think you're ready.